Lactoferrin is known as an iron-binding protein occurring, in vivo, in lacrima, saliva, peripheral blood and milk and the like of animals inclusive of human beings. It is said that the lactoferrin content in cow's milk is 1/10 of that in human milk. It is also known that bovine lactoferrin has antibacterial activity to certain harmful microorganisms belonging to the genuses of Escherichia, Candida and Clostridium and the like [cf: Welsh, J. K. and J. T. May; Journal of Pediatrics; Vol. 94; Page 1; 1979].
It has been also reported that bovine apolactoferrin, which is obtainable by unbinding iron from lactoferrin originating from cow's milk, may inhibit proliferation of certain harmful microorganisms belonging to the genuses of Escherichia, Staphylococcus and Enterococcus and the like in synthetic culture medium with a concentration of 0.5-30 mg apolactoferrin per ml media [Nonnecke, B. J. and K. L. Smith; Journal of Dairy Science; Vol. 67; Page 606; 1984].
It has been considered in general that apolactoferrin may act to inhibit proliferation of microorganisms, which require iron strongly, due to chelation of iron with apolactoferrin in the environment thereof. A considerable quantity of apolactoferrin is needed, however, when apolactoferrin is utilized alone, to show its antibacterial activity. Consequently, there was a limitation of its usefulness.
It has been attempted to increase the antibacterial activity of apolactoferrin. For example, it is proposed to use lactoferrin together with lysozyme [Japanese Unexamined Patent Application Gazette No. 62(1987)249931]. It has been also reported that copresence of lactoferrin and secretory IgA may augment antibacterial activity [Stephens, S., J. M. Dolby, J. Montreuil and G. Spik; Immunology; Vol. 41; Page 597; 1980]. However, these prior art disclosures have defects in that they need additional effective components which are difficult to obtain in a quantity of industrial scale in a reasonable cost.
On the other hand, it has been known that human lactoferrin occurring in human milk may promote proliferation of Bifidobacteria which are typical and useful microorganisms found in the human intestine [Kodama; Nihon Shounika Gakukaihou (The Journal of Japanese Pediatric Society); Vol. 87; Page 1000; 1983]. However, it is difficult to obtain human lactoferrin in a quantity of industrial scale in a reasonable cost.